I have dreamt about a game that allows you to manipulate the world itself, to be allowed to travel virtually anywhere, and do whatever you'd like. I intend on making this possible in the game here: Morden - A Lone World: This game is set in a dark manner, a very dark one, almost everybody is dead, and you have no idea where you are. You have no idea what to do, what to say, and what to think. My thoughts being, you will be able to do virtually anything you want. Oh, I forgot to mention, this will be a zombie game. But it will not be that obvious. Different zombies will have different behaviours, I intend on making the player be able to interact in a violent and or not violent way towards these creatures. Also, there will be other struggles within, the struggle to find food, water, and everything a living thing needs. If you find any flaws in this idea, please tell me, and if you like where this idea is going, please contact @ maxmordolm@gmail.com or my blog http://mordolmsworld.blogspot.com/

So, sort of like Halo's edit map type scenario, but a bit more extreme like adding in large terrain, which I find a huge problem. Most likely you will have to add restrictions.
I like the idea of manipulating a world, but personally zombies is a stale theme now a days along with the food and survival things. It just seems like DayZ, but you make your maps.